How do you best use XP enhancing items?

Fuzzy can only speak from experience of using the hyper at higher levels, and personally would only suggest using in Forgotten Frostland, but me take a stab at answering your questions...

1. What do you do during the buff? This one be sorta 50/50.. you CAN grind like mad, but there is a "pause" option available once the hyper is activated. If you wanted, you could simply pause the hyper-time when running back and forth to turn in old or collect new quest. (but be aware, each time you pause the hyper, using this feature consumes 1 minute of the remaining time)
   
   
2. Use at any level? To get the most bang-for-your-buck the best place to use them is Forgotten Frostland on 12x once you get to lvl 85 or find a party willing to take you into the instance at a lower lvl. That being said, there is nothing stopping you from activating them at lvl1 if you so choose.
   
   
3. Can you log out? Yes, you can log out. Just put your hyper-time on pause (again, this action will consume 1 minute of remaining hyper-time) and log out as normal. While you are gone both your buffer time and exhaustion time will erode (gotta like that) but your remaining hyper-time will stay the same until the next time you choose to activate it.
   
   
4. Which ones? This would be down to personal pref and/or how many you are able to get your hands on. 12x for 1hr work best in Frostland since you can get multiple runs out of 1 hour of hyper-time. If you decide you want to try and use them for grinding at lower lvl's.... it would seem to make sense to take the most balanced option that gives at least a few hours of hyper at less of a multiplier.. then just activate/pause as you quest to get the most out of them. (last bit there just Fuzzy's personal opinion)
   
   
5. Solo? Again, just a subjective opinion, but killing as much as possible as fast as possible seems to be the best use of them so AoE grinding with a party or how ever you wish to work it makes sense...

Hope that helps ya...
b:thanks